The polymerization of gaseous olefins such as ethylene and propylene in the vapor phase in a fluidized bed process offers attractively-low manufacturing costs in that no costs are incurred to recover and purify solvents. In the process, ethylene or propylene gas is fed into the bottom of the reactor and polymerization catalyst particles are blown into the reaction zone with an inert gas such as nitrogen. The ethylene polymerizes on the polymerization catalyst particles which are withdrawn from the bottom of the reactor. The unpolymerized ethylene is withdrawn from the top of the reactor as an overhead stream and is recycled.
A shortcoming of the process is that the conversion of ethylene to ethylene polymer is relatively low. As an inert gas is employed to blow the polymerization catalyst particles into the reaction zone, such inert gas accumulates in the reaction system. Periodically, a portion of the recycled ethylene gas must be purged to prevent too great a buildup of inert gas in the polymerization zone. The venting of the ethylene gas, of course is a cost burden on the process. In view of this fact, it would be desirable to have available to the art methods for introducing the polymerization catalyst particles into the reaction zone without the attendant accumulation of inert gas.